The diffusion of sulfur dioxide, a common atmospheric pollutant, through boxboards used to make up archival storage boxes has been measured, and diffusion constants were calculated from the resulting data. For the most common boxes used by the National Archives and Records Administration, a diffusion constant of about 0.001 cm²/sec is measured for SO₂ in the concentration range 10-150 ppm. For this 15-fold change in gas concentration, less than 25per thousand variation in the calculated diffusion constant was found. These results are discussed in terms of Passaglia's model of the microenvironment provided by these boxboards as used in archival storage.